This proposal continues our longstanding interest in the role of metals in the antitumor properties of compounds which can bind metal ions. Our approach is to do relavant inorganic chemistry, biochemistry, and cellular studies on the compounds of interest to build up a self-consistent, integrated picture of how metal-binding drugs and their metal complexes interact with cells to cause cytotoxicity. In the application, we continue our studies of bleomycin (Blm) to test the hypothesis that to become an active cytotoxic agent, Blm must bind intracellular Fe(II) and in the presence of oxygen carry out the strand scission of DNA. The experimental focus of the research is in the metabolism and speciation of Blm and its metal complexes in Ehrlich cells. The use of high performance liquid chromatography and atomic absorption spectrophotometry of fractions of cells exposed to radiolabeled drug and metal will be a major technical approach to this problem. This will be complemented by investigations on the whole cell exposed to (metallo)drug, in which state-of-the-art Electron Spin Resonance (ESR) spectroscopy will be employed. These studies will be aided by the use of Fe-depleted cells, studies of the comparative properties of Blm and active metallo-bleomycins, investigations of inactive CoBlm, and by the examination of functionally-active, modified bleomycins whose structures have been defined by NMR spectroscopy.